McNeill was a student of Arnold Toynbee, who instead emphasized separation and conflict as key drivers of world history. In a way, McNeill spent his career disagreeing with his teacher, thus living out the dreams of countless frustrated students.
Plagues and Peoples applies McNeill’s interconnectedness emphasis to disease as an engine of world history. This is of obvious interest in the wake of COVID-19. What can we learn from how other societies have dealt with plagues? What were mistakes we can avoid? What things worked that we can adapt to our own time?
As a big-picture world historian, McNeill’s book begins in prehistory and goes all the way up to modern times. In a later edition’s preface, McNeill briefly analyzes the AIDS epidemic, although in this reviewer’s opinion, that part has not aged well.
The rest of the book mostly has. That said, its focus on disease means that McNeill, at least in Plagues and Peoples, gives short shrift to other historical factors This is a forgivable sin; books have only so much space, and McNeill gives them plenty of attention in other works such, as his mistitled The Rise of the West: A History of the Human Community (1963), which spends more time out of the West than in it. But it is up to the reader to remember that history is nearly always multicausal.
As population grew after the agricultural revolution, long-separated peoples gradually came into contact with each other. Each group had suffered from its own local diseases. These depended on climate, geography, livestock, and agricultural choices. Tropical diseases rarely adapt well to cold climates, and vice versa.
An early obstacle to animal domestication was disease transmission between species. Over time, humans built up immune tolerances to their animal companions’ diseases. But different regions had different domesticated species, and hence different immunities. This caused outbreaks when people with different domesticated animals made first contact. Rice farmers, who spend much of their time wading through standing water, face a very different disease mix than farmers of grains or legumes, who deal with land-based diseases transmitted from insects, pests, and animal feces.
When different cultures first came into contact, there were often terrible outbreaks at their borders—this happened throughout Eurasia as agriculture and cities spread across the continent. If people near borders continued to interact, they built up mutual immunities to each other’s diseases, and could then benefit from trade, specialization, and cultural exchange.
But if there were long breaks in contact for whatever reason, the immunization process might have to start all over again. And sometimes people might decide it wasn’t worth the bother. These types of local disease-related decisions could impact generations of economic well-being, as well as decisions of war and peace.
This same process happened on a much larger scale after Columbus. It was also far more intense. The wild versions of the Americas’ domesticated animals, such as llamas and alpacas, did not live densely together enough to sustain highly infectious diseases. That means they didn’t pass them along to humans during domestication. So not only were Amerindian civilizations capable of greater density with fewer diseases than was possible in Europe, people in the Americas also had far fewer antibodies. This is one reason why contact with Europeans and their animals hit so hard.
Some diseases also require a minimum population density to survive. This includes diseases where the sufferer gains lifelong immunity after illness, such as chicken pox. Such diseases need constant access to fresh hosts who have not yet developed immunity. Often the only places with enough density and fresh hosts are cities. Cities, it turns out, were a major development for more than just humans.
At the macro level, high disease rates in cities played a major role in millennia of urban-rural interactions. There were fewer diseases out in the country, so population growth there was often rapid. In cities, deaths usually outpaced births until modern times—and modern sanitation. Cities depended on rural migration to maintain population—at precisely the same time as rural population growth was too high to bear. So rural-to-urban migration balanced out both environments.
This delicate equilibrium was often upset by wars, famines, and other non-disease factors. But this equilibrating tendency was the norm for most of history, and disease rates played a major role in the rate of urbanization until the last century or so.
This had special importance in post-classical Europe. Feudal ties bound rural peasants to nobles and kings. But the rise of cities, who often answered to no king, offered refuge to peasants, who continued to migrate away from kings into cities. A custom evolved whereby an escaped serf who was able to live in a city for a year and a day without being captured was legally emancipated. This is where the phrase “city air makes one free” came from, as well as city names such as Freiburg (“free town”). Disease rates, which kept cities constantly in need of fresh migrants, played an important role in this cultural and political dynamic.
Moreover, these power struggles, with disease always operating in the background, prevented kings from becoming too strong. These checks and balances eventually led to city- and democracy-based modernity as we know it today.
One of the most interesting concepts in Plagues and Peoples is McNeill’s comparison of microparasites and macroparasites. Viral and bacterial pathogens are microparasites. Some of their behavioral tendencies repeat themselves at a macro level in humans. An example of this is in McNeill’s theory of government.
McNeill’s theory of the origins of the state is similar Mancur Olson’s stationary bandit theory, but with a disease-centered twist. McNeill observes that diseases that are too lethal don’t survive for very long. They kill their host so quickly that they cannot spread. This is why Ebola breakouts, though terrifying, tend not to spread very far. At the macroparasite level, a bandit who completely destroys an agricultural settlement feeds himself for a day. But after that, like Ebola, he might have a hard time finding food.
More “successful” diseases such as colds, flus, or malaria make their hosts ill enough to exhibit contagion-spreading behaviors such as coughing, sneezing, or diarrhea. But they don’t kill them. Or at least, death does not come quickly enough to stop the pathogen’s spread. In the microparasite world, a milder human bandit also does much better for himself. He takes enough to feed himself, but not enough to starve his “hosts.”
The concept of immunity also plays a role. If the bandit “immunizes” his hosts against competing bandits, they gain security. The bandit not only gains a steady food source, but his immunized villagers may actually be happy to have him around; a chronic but mild illness is preferable to sudden death.
Analogous to biological natural selection, destructive roving bandits eventually gave way to milder stationary bandits, who gradually took on the trappings and functions of proper governments. And in social evolution, change need not mean death. A simple change in strategy is enough for a roving bandit to change into a stationary bandit. From this selection process, the earliest states emerged. One needn’t take the disease analogy too literally for it to shed useful light on an important process in human history. James C. Scott’s book Against the Grain: A Deep History of the Earliest States has much to offer readers interested in pursuing this direction further.
McNeill then applies this framework throughout world history. Confucianism arose in China as a successful macroparasitic adaptation to “keep exactions imposed upon the peasantry within traditional and, under most circumstances, tolerable limits.” (p. 101) The Confucian examination system limited the number of government officials, and imposed cultural, ethical, and institutional restraints on their behavior. The Confucian system kept Leviathan properly shackled, as Daron Acemoglu and James A. Robinson might argue (see my review of their recent book The Narrow Corridor: States, Societies, and the Fate of Liberty).
This dynamic, McNeill theorizes, might explain why the earliest known governments in Egypt and Mesopotamia were highly despotic, even compared to later absolute monarchies.
The 14th century bubonic plague pandemic known as the Black Death happened as it did in large part due to interconnectedness. As always in history, there were many factors. The plague bacillus tended to be stable only in rodent communities in remote areas. The rise of the Mongols and their fast-moving horses not only displaced many of these rodent communities, but their swift-moving horses—and enticing grains and other foods—drove rodents across the Eurasian continent. Independently, “Improvements in ship design occurring in the 13th century made year-round sailing normal for the first time,” which “offered securer and more far-ranging vehicles for rats.” (pp. 176-177). These multiple engines of interconnectedness made plague vectors spread faster and farther than they otherwise would have.
The plague response also has a potential lesson for today’s policy makers. On p. 195, McNeill observes:
In contrast to the rigidities of the church, city governments, especially in Italy, responded rather quickly to the challenges presented by devastating disease. Magistrates learned how to cope at the practical level, organizing burials, safeguarding food deliveries, hiring doctors, and establishing other regulations for public and private behavior in time of plague.
The Church was a very different creature than today’s federal or national governments, but the larger principle stands: smaller, closer governments tend to be more responsive than larger, distant ones. People today expect more of Washington than it could possibly deliver during the time of COVID-19. Effective responses will instead tend to come at the individual, local, and state levels.